Why does CBC decryption with a wrong IV still give readable results?More exactly... in case 1: the plain text is encrypted using IV = E(R), decryption encrypts R as block 1 then uses E(R) for block 2. In case 2: the algorithm is run first on IV (to encrypt it) giving E(R) so the plaintext is encrypted using E(E(R)). Since E(R) is written as the first block of the file, when decrypting, E(E(R)) ends up being used for the the plaintext, thus correct decrypting.